Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	$ (9,665)	$ (9,941)	$ (9,665)	$ (9,941)		$ (10,855)
Other Comprehensive Income (Loss), Net of Tax	11	284	1,190	305
Derivative instruments	32	38	148	(100)
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	59	48	59	48	$ 72	104	$ 40	$ 64
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(10)	35	(25)	39
Other Comprehensive Income (Loss), Tax	3	(8)	5	(10)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(7)	27	(20)	29
Other Comprehensive Income (Loss), Net of Tax	(13)	8	(45)	(16)
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(8)	(25)	(33)	(59)
Reclassification from AOCI, Current Period, Tax	2	6	8	14
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(6)	(19)	(25)	(45)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(1,275)	(1,144)	(1,275)	(1,144)	(1,118)	(930)	(1,235)	(1,135)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(148)	116	(298)	18
Other Comprehensive Income (Loss), Tax	(8)	4	(43)	18
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(156)	120	(341)	36
Other Comprehensive Income (Loss), Net of Tax	(157)	91	(345)	(9)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(1)	(29)	(4)	(45)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(8,127)	(8,351)	(8,127)	(8,351)	(8,276)	(9,559)	(8,498)	(8,781)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	2	2	1,270	2
Other Comprehensive Income (Loss), Tax	0	0	(298)	0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	2	2	972	2
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	191	188	583	557
Reclassification from AOCI, Current Period, Tax	(44)	(43)	(123)	(129)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	147	145	460	428
Other Comprehensive Income (Loss), Net of Tax	149	147	1,432	430
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(322)	(494)	(322)	(494)	$ (354)	$ (470)	$ (532)	$ (394)
Other Comprehensive Income (Loss), before Reclassifications, before Tax	55	45	167	(114)
Other Comprehensive Income (Loss), Tax	(9)	(10)	(10)	(2)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	46	35	157	(116)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	(16)	5	(10)	24
Reclassification from AOCI, Current Period, Tax	2	(2)	1	(8)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(14)	3	(9)	16
Derivative instruments	$ 32	$ 38	$ 148	$ (100)